More safety concerns have been raised over the Hinkley B nuclear power station in Somerset after a malfunction in one of its vital control rods forced it to shut down for more than 72 hours. British Energy, which runs the atomic plant, refuted suggestions the incident prompted an emergency shutdown and said the switching off of the plant at huge expense was a controlled manual shut down to carry out repairs.

The problem occurred at about 10am on Saturday and the reactor was not running again until Tuesday afternoon.

The B reactor has 81 carbon control rods which are released into the graphite core of the reactor to temper the fusion process, allowing the plant to be effectively turned off.

On Saturday morning, an electrical failure in the equipment holding one of the rods let it fall into the reactor. The rest of the rods were then deliberately inserted into the core so the faulty equipment could be repaired and the rod replaced.

Earlier this month, documents were released showing that Government watchdogs had expressed fears about the state of cracks in the graphite core at Hinkley B. Campaigners said it was cause to shut the plant for good, but nuclear bosses insisted the issue had been resolved and the report taken out of context.

British Energy said Saturday's incident had nothing to do with the graphite core, but Jo Brown, from the Stop Hinkley group, remains unimpressed. "It is another worry to add to the list," she said